Here are a few pictures of the pair of Lehman seismometers that I am currently operating in Vermont. The construction is primarily of square aluminum tube that you can get in most big box hardware stores.
The two instruments differ in the construction of their motors and in the sensors used. The East-West device has an LVDT sensor while the North-South machine uses a photo-optical sensor. Both machines have the same sensitivity.
That is a six inch scale on the workbench in front of the seismometer.
Here is a picture of the upper pivot. It is made of crossed pieces of .001" thick steel shim stock. You can see the wires from the damping motor coil where they cross over the pivot.
The last picture in this group shows the two instruments in their insulated box. There are heaters on the top of the box. The temperature in the box is regulated to 80°F at a point just over the instruments. The sheet aluminum on top of the units is there to reflect thermal radiation from the heaters.
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